I highly recommend Mass Effect, Oblivion (which still hasn’t dropped in price ??), Assassin’s Creed, Gears of War I love the online play honestly I find myself playing it over Halo3 most days, Halo 3 is awesome for like if you have big parties, a few weeks back I had 20 or so friends over with a bunch of tv’s set up and xbox’s and we played halo like all night and it’s a blast seriously. Gears of War online is just more team based than halo3, in halo3 i notice people just do their own thing.
The only game I really think I wanna get is BioShock based on the demo and it got 10s in like every review I’ve read.
…So I recommend all those game. I also recommend NBA 2K8 and Fight Night 3 which I play sometimes.